Iron synthesis catalyst



INVENTOR Henry G. N Gra lh 41 2 FM M11. Ilw..

United States Patent IRON SYNTHESIS CATALYST Henry G. McGrath, Union, N.J., assignor to The M. W. Kellogg Company, Jersey City, N. J., acorporation of Delaware Original application February 1, 1947, SerialNo. 725,835,

new Patent No. 2,598,647, dated May 27, 1952. Divided and thisapplication April 14, 1052, Serial No. 282,150

4 Claims. (Cl. 252-474) This invention relates to the synthesis oforganic compounds. In one aspect this invention relates to thehydrogenation of an oxide of carbon in the presence of a hydrogenationcatalyst to produce hydrocarbons and oxygenated organic compounds. Moreparticularly in this aspect the invention relates to the hydrogenationof carbon monoxide in the presence of an iron catalyst of a specificcomposition under conditions to produce a relatively high yield ofoxygenated compounds. In an other aspect this invention relates to thehydrogenation of carbon monoxide in the presence of an iron catalyst ofa particular composition under conditions to produce a relatively highyield of hydrocarbons useful as motor fuel. This application is adivision of application Serial No. 725,835, filed February 1, 1947, nowissued as Patent No. 2,598,647.

It has been known for some time that hydrogen and carbon monoxide may bemade to react exothermically in the presence of catalysts under specificreaction conditions to form hydrocarbons and oxygenated compounds havingmore than one carbon atom per molecule. In general, the synthesis ofthese organic compounds by the hydrogenation of carbon monoxide isaccomplished in the presence of a metal or an oxide of a metal chosenfrom group VIII of the periodic table as a catalyst, at pressures belowabout 500 pounds per square inch gage and at temperatures below about750 F. for the production of hydrocarbons and at pressures between about1,000 and about 10,000 pounds per square inch gage and at temperaturesabove 750 F. for the production of oxygenated compounds.

The synthesis feed gas or reaction mixture comprises a mixture of aboutone to two mols of hydrogen per mol of carbon monoxide and may beprepared by the catalytic conversion of natural gas, steam, and carbondioxide.

Various methods have been practiced to effect the reaction of hydrogenand carbon monoxide to produce organic compounds. Among these methodsare those known as fixed-bed catalyst operations and fluid-bed catalystoperations. The fixed-bed operation comprises passing a reaction mixtureof hydrogen and carbon mon- "ice oxide through a stationary bed ofcatalyst in a reaction zone, and the fluid-bed operation comprisespassing a reaction mixture through a finely divided catalyst masssuspended in the reaction mixture in the reaction zone.

It is an object of this invention to provide a process for the synthesisof organic compounds having more than one carbon atom per molecule.

It is another object of this invention to provide a process for theproduction of oxygenated compounds in a relatively high yield by thereaction of carbon monoxide and hydrogen in the presence of ahydrogenation catalyst.

Another object of this invention is to provide a process for theproduction of hydrocarbons useful as a motor fuel in relatively highyield by the reaction of carbon monoxide and hydrogen in the presence ofa hydrogenation catalyst.

Still another object of this invention is to provide a novel catalystfor the hydrogenation of carbon monoxide.

A further object of this invention is to provide a method for producinga hydrogenation catalyst useful for the hydrogenation of carbonmonoxide.

It is still a further object of this invention to provide a particularnovel catalyst adapted to the fluidized process for the hydrogenation ofcarbon monoxide to produce a particular organic compound.

Yet another object is to provide a process for the synthesis of organicacids.

Various other objects and advantages will become apparent to thoseskilled in the art from the accompanying description and disclosure.

According to a preferred embodiment of this invention, 1 have found thata metal or metal oxide hydrogenation catalyst containing between about0.1 percent and about 2.5 percent by Weight of an oxide of potassium isvery effective for the hydrogenation of an oxide of carbon to produce ahigh yield of organic compounds having more than one carbon atom permolecule. For maximum yields and selectivity, a metallic iron or ironoxide catalyst containing between about 0.2 and about 2.0 percent byweight potassium oxide, K20, is preferred. A potassium oxide contentabove about 2.5 weight percent results in excessive formation of wax onthe catalyst, which decreases the activity and life of the catalyst;while a potassium oxide content below about 0.1 Weight percent resultsin substantially increased yields of carbon dioxide, methane, ethane,and other low molecular weight hydrocarbons.

It has further been found according to this invention that the amount ofpotassium oxide in the catalyst is critical with respect to the type ofproduct produced. Thus, for the production of oxygenated compounds,especially the relatively high molecular weight alcohols and organicacids, the catalyst must contain at least about 0.8 weight percent, andpreferably between about 1.0 and about 1.5 weight percent potassiumoxide. When it is desired to produce relatively high molecular weight 3hydrocarbons accompanied by a minimum amount of oxygenated compounds, ithas been found that the catalyst must contain between about 0.2 percentand about 0.7 percent potassium oxide. The percent K20 is based on theelementary metal content of the catalyst.

A high alkali iron catalyst containing between about 0.8 percent andabout 1.5 percent K20 produces a much larger amount of oxygenatedcompounds than a metallic iron catalyst of lower potassium oxide contentunder comparable reaction conditions. In fact, in some instances, asmuch as four or five times as much oxygenated compounds are produced bysuch a high alkali catalyst as with a lower alkali catalyst. Of theoxygenated compounds produced with the high alkali catalyst, the normalalcohols, such as ethanol, propanol, butanol, and pentanol, along withsuch organic acids as acetic, propionic, and butyric acids comprise themajor portion of the organic compounds. In contrast, with a low alkalicatalyst substantially negligible amounts of organic acids are producedand generally relatively smaller amounts of oxygenated compounds areproduced. It has also been noted that with the high alkali catalyst ofthe present invention, a substantial proportion of the relatively lowmolecular weight hydrocarbons produced are olefinic and are present inthe product in a relatively larger proportion than in the product of thelow alkali catalyst. It is possible to operate with the high alkalicatalyst at relatively higher temperatures than is possible with lowalkali catalysts without excessive formation of coke on the catalyst.

On the other hand, it has been found that z low alkali iron catalystcontaining between about 0.2 percent and about 0.7 percent potassiumoxide produces the maximum yield of hydrocarbons. In the hydrogenationof carbon monoxide with a low alkali catalyst according to thisinvention the maximum yield of hydrocarbons of high quality boilingwithin the gasoline range are obtained. Furthermore, the low alkali ironcatalyst produces a hydrocarbon fraction useful as a diesel fuel of muchhigher quality than that produced with a high alkali catalyst.Relatively higher space velocities for somewhat lower temperatures maybe used with the low alkali catalyst than with the high alkali catalystfor an equivalent conversion of carbon monoxide.

Although potassium oxide has been found to be the much preferredactivating compound when incorporated with a hydrogenation catalystcomprising a metal and/ or metal oxide, other potassium compounds andother inorganic compounds of alkali metals and alkaline earths, such assodium, barium, and lithium, are capable of being incorporated with thehydrogenation catalyst in above ranges previously qualified with respectto K20 when calculated as the oxide and based on total metal.Preferably, such activating compounds of alkali metals and alkalineearths contain oxygen in the form of the hydroxide, carbonate, sulphate,silicate, phosphate, aluminate, 'chromate, nitrate, and borate.Potassium carbonate, nitrate, hydroxide, and chloride have shown verygood results, particularly when these compounds were incorporated with ahydrogenation catalyst comprising iron in quantities greater than about0.8 weight percent (calculated as K20) high yields of oxygenated organiccompounds were produced. Mixtures of these compounds may be used as theactivating material without departing from the scope of this invention,and when mixtures are used the alkali content calculated as the oxide isconsidered as either the total quantity of com pounds or the quantity ofany single compound.

The activating compound, such as K20, may be incorporated with thehydrogenation catalyst in a solid solution or a fused conditiontherewith, or it may be merely on the surface of the hydrogenationcatalyst uncombined therewith in any way. For example, a naturallyoccurring magnetite may be mixed with an appropriate amount of potassiumhydroxide or potassium carbonate and the resulting mixture fused. Thefused mixture is then pulverized and reduced with hydrogen at atemperature between about 900 F. and about 1600" F. In this manner ofpreparation the potassium oxide is present in the ultimate catalyst in afused condition with iron. In another manner of preparation in which thealkali is on the surface of the catalyst uncombined with the iron,naturally occurring magnetite is fused, pulverized, mixed with potassiumcarbonate, and the resulting mixture reduced.

The catalyst of this invention may be employed in stationary orfixed-bed condition, as well as the fluidized or fluid-bed condition;however, it is much preferred to employ it in a fluidized condition.

A preferred embodiment of this invention involves flowing a gaseousmixture comprising hydrogen and a carbon oxide to be hydrogenatedupwardly in a reaction zone in contact with a mass of finely dividedmetallic iron catalyst containing an appropriate amount of potassiumoxide for producing the desired product. The hydrogen and carbon oxidereactants are passed as gases through the reaction zone, underconditions effective to react all, or a portion, of the carbon oxidereactant. The gaseous mixture is passed upwardly through the mass ofcatalyst at a velocity sufficient to suspend or entrain the catalystmass in the gas stream. Preferably, the velocity of the gas streampassing through the re action zone is sufliciently low to maintain thecatalyst mass in a dense, fluidized pseudoliquid condition. However, thevelocity may be suiiiciently high to entrain at least a substantialportion of the finely divided catalyst in the gas stream to form acontinuous catalyst phase which circulates with the flowing gas stream,without departing from the scope of this invention. In the formercondition the catalyst mass may be said to be suspended in the gasstream, but not entrained therein in the sense that there is movement ofthe catalyst mass as such in the direction of flow of the gas stream.When operating with the catalyst in the pseudo-liquid condition it ispreferred to maintain the upward velocity of the gas stream suflicientlyhigh to maintain the fluidized catalyst mass in a highly turbulentcondition in which the catalyst particles circulate at a high rate inthe pseudoliquid mass. In this pseudo-liquid condition of operation asmall proportion of catalyst in the fluidized mass may become entrainedin the gas stream emerging from the upper surface of the fluidized masswhereby catalyst thus entrained is carried away from the mass.

In the present process it is preferred to employ the hydrogen and carbonoxide in ratios such that there is an excess of hydrogen. Therefore, thecharging rate in the present process is defined by reference to the rateat which the carbon oxide is charged, in terms of standard cubic feet,in the gas form, of the carbon oxide, per hour per pound of the metalcatalyst in the dense pseudo-liquid mass of catalyst in the reactionzone. The fluidized process is preferably operated at a minimum spacevelocity equivalent to charging rate of about 1.0 standard cubic foot ofthe carbon oxide reactant, per hour, per pound of the metal catalyst inthe dense catalyst phase. A standard cubic foot of the carbon oxide isthat quantity of a normally gaseous carbon oxide which would occupy onecubic foot at atmospheric pressure at 60 F, or an equivalent quantity ofa normally liquid carbon oxide reactant. Generally, with fluidized densephase operation and pressures between and 300 pounds per square inchgage with the high alkali catalyst, a space velocity between about 4 andabout 10 standard cubic feet of the carbon oxide reactant, per hour perpound of the iron catalyst is used. With the low alkali catalyst a spacevelocity between about 10 and about 25 is used.

The catalyst employed in the present invention is a finely dividedpowder comprising a metal and/or metal oxide containing the appropriateamount of potassium oxide which is, or becomes in the reaction zoneacatalyst for the reaction, or a mixture of such metal or metal oxide andother catalytic materials or non-catalytic materials. While the catalystpowder consists essen tially of such catalytic metal or metal oxidecontaining potassium oxide it may include also a minor amount ofpromoting ingredients, such as alumina, silica, titania, thoria,manganese oxide, magnesia, etc.

In this specification and claims the catalyst employed is described byreference to its chemical condition when first contacted with thereactants.

The catalyst is employed in a fine state of sub-division. Preferably,the powdered catalyst initially contains no more than a minor proportionby weight of material whose particle size is greater than 250 microns.Preferably also, the greater proportion of the catalyst mass comprisesmaterial whose particle size is smaller than 100 microns, including atleast weight percent of the material in particle sizes smaller than 40microns. A highly desirable powdered catalyst comprises at least 75percent by weight of material smaller than 150 microns in particle size,and at least 25 percent by weight smaller than about 40 microns inparticle size.

In the preferred form of the invention with the catalyst present in apseudo-liquid condition, the powdered catalyst mass is maintained in areactor substantially larger than the volume occupied by the catalystmass in the fluidized condition. In this operation all but a minorproportion of the catalyst mass is contained in the dense fluidizedpseudo-liquid mass, which may be designated as the dense phase of thecatalyst. The dense phase of the catalyst occupies the lower part of thereactor while that part of the reactor above the dense phase is occupiedby a mixture of gases and powdered catalyst in which the catalystconcentration is much lower, and of a different order of magnitude, thanthe concentration of the catalyst in the dense phase. This diifuse phasemay be said to be a disengaging zone in which the solids lifted abovethe dense phase by the gas stream are disengaged therefrom and returnedto the dense phase to the extent that such solids are present in thediffuse phase in excess of the carrying capacity of the gas stream atthe superficial velocity of the gas stream. The latter is the velocityat which the gas stream would flow through the reactor in the absence ofcatalyst. In the dense phase the concentration of the catalyst in thegas stream varies from a maximum near the gas inlet to a minimum in theupper part of this phase. Likewise the concentration of catalyst in thediffuse phase varies from a maximum near the upper surface of the densephase to a minimum in the upper part of the reactor. Between the densephase of high average concentration and the diifuse phase of low averageconcentration there is a relatively narrow zone in which theconcentration of solids in the gas stream changes in a short space fromthe high concentration of the dense phase to the low concentration ofthe diffuse phase. This zone has the appearance of an interface betweentwo visually distinct phases.

This operation ordinarily involves employment of catalyst powders andgas velocities such that a relatively small portion of the densefluidized catalyst mass is carried away by entrainment, and it isnecessary, therefore, to provide means in the reactor for separatingsuch entrained catalyst and returning it to the dense phase, or toprovide means externally of the gas reactor to separate entrainedcatalyst from the gas stream and return it to the reactor, or otherwiseto recover catalyst from the product. gas stream.

the desired volume of fluidized catalyst in the reaction zone.

The pseudo-liquid operation in which the finely powdered catalyst isemployed in a form consisting of the metallic iron catalyst andcontaining at most minor proportions of promoting agents, other thanpotassium oxide, provides very high catalyst concentrations in thereaction zone. The employment of the finely powdered metal catalyst in afluidized bed with efiicient cooling means also is a factor inpermitting the use of high catalyst concentrat-ions, since itfacilitates the removal of heat from the relatively concentratedreaction zone. The pseudo-liquid operation, employing the finely dividedmetal catalyst, results in initial catalyst concentrations of at least30 pounds per cubic-foot of the fluidized dense catalyst phase, whilethe preferred gas velocities result in initial concentrations of 40' to120, or more, pounds per cubic foot of dense phase. It will beunderstood that these figures refer to the initial average concentrationin the dense phase. The accumulation of reaction products on thecatalyst particles as the operation proceeds reduces the catalystdensity and increases the bulk of the dense fluidized mass.

With an iron catalyst containing an oxide of potassium, temperatures inthe range of about 350 F. to about 750 F. are employed. Usually about 30F. to about 50 F. higher temperatures are necessary with the high alkalicatalyst than with the low alkali catalyst. With the iron catalyst,pressures between atmospheric pressure and the maximum pressure at whichcondensation is avoided may be employed. It is desirable, however, toemploy pressures of at least 50 p. s. i. and preferably about 150 toabout 500 p. s. i.

In this specification, pressures are expressed as pounds per square inchgage and gas volumes as cubic feet measured at 60 F. and atmosphericpressure.

The linear velocity of the gas stream passing upwardly through the densephase is conveniently expressed in terms of the superficial velocity,which is the linear velocity the charge gas stream would assume ifpassed through the reactor in the absence of catalyst. This superficialvelocity takes into account the shrinkage in volume caused by thereaction and is, preferably, in the range of from 0.1 to 10 feet persecond. When operating with a continuous catalyst phase in which thecatalyst is entrained in the flowing gaseous mixture, velocities as highas 40 feet per second may be used.

The reactants are passed into and through the reaction zone at a spacevelocity equivalent to at least 1.0 standard cubic feet of carbon oxideper hour per pound of metal catalyst in the dense catalyst phase. In thehydrogenation of carbon monoxide with the iron catalyst it is preferredto operate at a space velocity equivalent to at least 2.0 standard cubicfeet of carbon monoxide per hour per pound of iron catalyst in the densecatalyst phase. The charging rate is defined by reference to the carbonmonoxide reactant, since the ratio of-the hydrogen reactant to thecarbon monoxide reactant in the charge gas may vary within wide limits.This ratio of hydrogen to carbon monoxide is usually in excess of about0.7:1

" and preferably'at least 1:1 and often as high as 10:1. At

When catalyst is permitted to pass out of the reactor by entrainment inthe gas stream in either the pseudoliquid operation or the continuousphase operation, it is necessary to return such catalyst to the reactor,or replace it with fresh or revivified catalyst, in' order to maintainthe 1:1 ratio the preferred charging rate of hydrogen and carbonmonoxide would, therefore, be at least 4.0 standard cubic feet per hourper pound of iron catalyst in the dense catalyst phase. At a 2:1 ratiothis preferred rate would be 6.0 standard cubic feet of hydrogen andcarbon monoxide. v

The volume of reactants per hour per volume of dense pseudo-liquidcatalyst phase depends upon the charge rate and also upon theconcentration of catalyst in the dense phase, the latter being affectedby the condition of the catalyst and the gas velocity. At the preferredgas velocities mentioned above for the pseudo-liquid operation, and whenemploying an iron catalyst, the minimum space a r-eases velocity may bedefined as 2 cubic feet of carbon monoxide per hour per pound of ironcatalyst.

According to a preferred modification of this invention a fresh feed gashaving an H2:CO ratio higher than the ratio in which .these compoundsare converted to other compounds is employed and the ratio of hydrogento carbon monoxide in the charge to the reactor is increased to thedesired figure by recycling a portion of the unconvertcd gas, afterremoval of part or all of the product liquid. A gas containing excesshydrogen is processed under conditions eflfective to react all, or aportion, of the carbon monoxide, and a portion of the product mixture,after removal of the greater part of the liquid product, is recycled involumetric ratios, to the fresh feed gas, of 0.5:1 to 10:1. Since in oneembodiment of this invention, a relatively large amount of oxygenatedcompounds are produced, a portion of the oxygenated organic compoundscomprising the relatively low boiling compounds, such as the ketones andaldehydes, are separated and recycled to the hydrogenation reaction toincrease the yield of oxygenated organic compounds of relatively highboiling point. A similar effect on the production of oxygenated organiccompounds is also accomplished by recycling unsaturated compounds, suchas olefins, which have been separated from the effiuent of thehydrogenation reaction. Unsaturated and oxygenated compounds fromsources other than the process itself may be introduced into thereaction without departing from the scope of this invention.

Fluid operations are carried out at temperature levels which arerelatively high as compared to those which would be permissible in fixedcatalyst bed operations under comparable operating conditions. Thisresults from the excellent heat transfer capacity of the fluidized massof finely divided iron or iron oxide and the efiect of excess hydrogenin minimizing carbon formation. It is preferred to operate at whatevertemperature level, in the range of 350 F. to 750 F., is necessary toeffect high conversion of carbon monoxide when treating a gas chargecontaining more hydrogen than carbon monoxide, at space velocitiesequivalent to at least 2 standard cubic feet of carbon monoxide per hourper pound of iron catalyst in the dense phase.

The invention will be described further by reference to the accompanyingdrawing which is a view in elevation, partly in section, of a reactoremployed in carrying out the present invention by a pseudo-liquidoperation, and by reference to specific examples of operations embodyingthe present invention and carried out in apparatus exemplified by thedrawing.

Referring to the drawing, reactor 1 consists of a length of extra heavy2-inch steel pipe which is about 240 inches long and has inside andoutside diameters of 1.95 inches and 2.50 inches, respectively. Reactor1 is connected by a conical section 2 to an inlet pipe 3 made of extraheavy-half-inch steel pipe having an inside diameter of 0.55 inch.Reactor 1 is connected at the top, by means of a conical section 4, withan enlarged conduit comprising a length of 8-inch extra heavy steel pipehaving an inside diameter of 7.63 inches. Conical section 4 and conduit5 constitute an enlarged extension of reactor 2 which facilitatesdisengagement of catalyst from the gas stream after passage of thelatter through the dense catalyst phase.

Conduit 5 is connected by means of a manifold 6 with conduits 7 and 8which comprise other sections of extra heavy 8-inch steel pipe. Conduits'7 and 8 contain filters 9 and 16 which are constructed of porousmaterial which is permeable to the gas and vapors emerging from thereaction zone but impermeable to the catalyst particles carried byentrainment in the gas stream. Filters 9 and 10 are cylindrical in shapeand closed at the bottom ends. They are dimensioned in relation toconduits 7 and 8 to provide a substantial annular space between thefilter and the inner wall of the enclosing conduit for the passage ofgases and vapors and entrained catalyst upwardly about the outer surfaceof the filter. The upper ends of filters 9 and 10 are mounted in closuremeans 11 and 12 ha manner whereby the gases and vapors must pass througheither filter 9 or filter 10 to reach exit pipes 13 and 14. Each offilters 9 and 10 is approximately 36 inches long and 4%. inches inouside diameter, .the filter walls being approximately of an inch thick.

The greater part of reactor 1 is enclosed in a jacket 15 which extendsfrom a point near the top of reactor 1 to a point sufficiently low toenclose the 3-inch length of conical section 2 and approximately 5inches of pipe 3. Jacket 15 comprises a length of extra heavy 4-inchsteel pipe having an inside diameter of 3.83 inches. The ends of jacket15 are formed by closing the ends of the 4-inch pipe in any suitablemanner, as shown. Access to the interior of jacket 15 is provided by anopening 16 in the top thereof through a 2-inch steel pipe. Jacket 15 isadapted to contain a body of liquid for temperature control purposes,such as water or Dowtherm. The vapors which are evolved by the heat ofreaction are withdrawn at 16, condensed, and returned to the body oftemperature control fluid in jacket 15. The condensate returned tojacket 15 may be introduced through line 16, or directly at a low point,adjacent pipe 3, by an inlet means not shown. The temperature controlfluid in jacket 15 is maintained under a pressure at which the liquidboils at the temperature desired in jacket 15. Heating coils, not shown,are provided in connection with jacket 15 to maintain the temperaturecontrol fluid therein at any desired temperature when it is desired toheat the contents of reactor 1.

in order to show all the essential parts of the reactor and associatedcatalyst separation means on a single sheet, a large proportion of theapparatus has been eliminated by the breaks at 17 and 18. For a clearunderstanding of the relative proportions of the apparatus, referencemay be had to the over-all length of the apparatus, from the bottom ofjacket 15 to exit pipes 13 and 14, which is about 310 inches. In each ofbreaks 17 and 18 the portion of the apparatus eliminated is identicalwith that portion shown immediately above and below each break.

In pseudo-liquid operations carried out in this apparatus the catalystrecovery means, comprising filters 9 and 10, are effective to separatesubstantially completely entrained catalyst from the outgoing stream ofgases and vapors. The disengagement of solids from the gas stream ispromoted by the lowered velocity of the gas stream in conduit 5 andremaining solids are separated on the outer surfaces of filters 9 and10. The latter are employed alternatively during the operation so thatthe stream of gases and vapors and entrained solids passes from conduit5 through either the left or right branches of manifold 6 into conduit'7 or conduit 8. During the alternate periods the filter which is not inuse is subjected to a back pressure of gas which is introduced at a ratesufficient to dislodge catalyst which has accumulated on the outersurface of the filter during the active period. Such blowback gas anddislodged catalyst fiow downwardly in the conduit enclosing the filterand into manifold 6, in which the blow-back gas is combined with thereaction mixture flowing upwardly from conduit 5. The greater part ofthe catalyst thus dislodged settles downwardly into the reactor and isthus returned for further use.

The amount of catalyst charged to the reactor initially is regulated,with reference to any preliminary treatment of the catalyst in thereactor and the gas velocity to be employed, whereby the upper level ofthe dense phase is substantially lower than the top of reactor 1. Duringthe operation the accumulation of deposited reaction products on thecatalyst particles may cause an expansion of the dense phase and a risein the height of the dense phase.

In the operation of the apparatus of the drawing the desired quantity ofpowdered catalyst is introduced directly into the reactor through asuitable connection, not shown, in conduit 5. After any desiredpreliminary activation treatment the temperature of the fluid in jacket15 is adjusted, by the heating means mentioned above and by the pressurecontrol means, to the temperature desired in jacket 15 during thereaction. After the catalyst mass has reached the reaction temperaturethe introduction of the reaction mixture through pipe 3 is initiated.During the reaction the liquid in jacket is maintained at the desiredtemperature by controlling its pressure. The reaction mixture may bepreheated approximately to the reaction temperature prior to itsintroduction through pipe 3, or the reactants may be heated to thereaction temperature through the passage thereof through that portion ofpipe 3 which is enclosed by jacket 15 and by contact with the hotcatalyst. In most of the operations described hereinafter it waspreferred to preheat the reaction mixture to temperatures of at least350 F.

Pipe 3 is dimensioned with respect to reactor 1 and the desiredsuperficial velocity whereby the velocity of the gases passing throughpipe 3 is sufliciently high to prevent the passage of solids downwardlyinto pipe 3 against the incoming gas stream. An orifice plate, nowshown, is provided in pipe 3 to prevent solids from passing downwardlyout of the reactor when the gas stream is not being introduced into pipe3.

In this apparatus operating runs were made to test the etficacy of thecatalyst of this invention in the treatment of a gas charge containinghydrogen and carbon monoxide to convert these reactants to hydrocarbonsand oxygenated compounds. In each operating run the alkali content ofthe catalyst was varied to test the efiect of various combinations ofcatalyst compositions. The results of each operating run are representedby the results observed during a stabilized period of operation under agiven combination of operating conditions. The conditions of operationand the results obtained in these op- EXAMPLE The catalysts for use inthese operations were prepared from an ammonia synthesis catalyst whichhad been prepared by fusion of alumina and potassium oxide in molteniron oxide to produce a mixture of iron oxide, alumina, and potassiumoxide. This material consisted principally of iron oxide and containedabout 2.9 percent alumina, about 3.4 percent potassium oxide, and lesseramounts of titania and silica. To prepare this material for use in thisimproved process it was first ground to a 6 to mesh size and thensubjected to leaching with water to remove the desired amount ofpotassium oxide. This treatment reduced the potassium oxide content fromabout 3.4 percent to about 0.3, about 0.6, and about 1.4 percent forthree separate catalysts based on Fe. The leached material was thendried at 210 F. and reduced in a stream of hydrogen.

In the reduction treatment a heated stream of hydrogen was passedthrough the granular mass of iron oxide, treated to remove water formedby the reduction reaction, and then recirculated. The temperature wasraised gradually and the reduction reaction was initiated at about 600F. to 800 F. The temperature of the catalyst mass was then raised toabout 1215 F. in two hours while continuing the flow of the hydrogenstream. During the next 4 hours the temperature was raised toapproximately 1285 F., during which time the reduction was substantiallycompleted, as evidenced by the practical cessation of water formation.The reduction is usually carried out at a temperature between about 1200F. and about 1400 F.

Each of the reduced catalysts were ground in an atmosphere of carbondioxide, first in a hand grinder and then in a ball mill, to produce apowder smaller than 250 microns and having approximately thefollowing-screen and roller analysis:

Table I ROLLER ANALYSIS Particle size, microns: Percent O-10 11.0

SCREEN ANALYSIS U. S. standard sieve: Percent +40 mesh Trace 40-60 Trace-120 Trace -140 Trace -200 13.5 ZOO-Pan 84.5

Between about 15,000 and 20,000 grams of catalyst thus prepared werecharged into reactor 1 through an inlet (not shown) in section 5. Duringthis operation the catalyst was maintained in the atmosphere of carbondioxide and a small stream of 1 or 2 cubic feet of carbon dioxide perhour was passed upwardly through reactor 1 to prevent packing of thecatalyst. After the catalyst was charged to reactor 1, the carbondioxide stream was replaced with a stream of hydrogen which was passedupwardly through reactor 1 at the rate of 15 to 20 cubic feet per hour.The reactor was then heated externally while hydrogen was passedupwardly through the reactor at this rate. When the desired temperaturewas rea-ched the hydrogen stream was replaced by a stream of synthesisgas consisting essentially of hydrogen and carbon monoxide in thedesired ratio. The synthesis gas was passed upwardly through reactor 1at the rates shown in the following tables. At the same time the outletpressure on the reactor was gradually increased to pounds and 250pounds, respectively.

An efiluent was removed from reactor 1 and unreacted reactants andproducts of the process were separated therefrom. The reaction productswere recovered for the most part by cooling the reaction mixture to roomtemperature or lower to obtain a condensate and by passing theuncondensed gases through an absorber, such as activated charcoal. Thecondensate comprised both heavy oil and water product fractions. Theheavy oil fraction contained a minor proportion of oxygenated compoundsand the water product fraction contained substantial amounts ofoxygenated compounds. The absorbed products were recovered by steamdistillation which yielded a light naphtha fraction, condensed water,and a gaseous fraction. The water contained additional oxygenatedcompounds. The gaseous fraction was almost entirely hydrocarbons havingthree to five carbon atoms per molecule. The yield of: the variousfractions were determined by measurement of the condensed product and byabsorption and combustion analysis of the gas from the condenser.Oxygenated compounds were recovered in most instances from the productsby distillation of the water product, by extraction of the condensed oilwith ethylene glycol and by water scrubbing the gaseous fraction. Therecovery of oxygenated organic products from the synthesis efiluent isdiscussed in considerably more detail in copending applications, SerialNos. 709,871, now Patent No. 2,470,782, and 709,872, filed November 14,1946, now Patent No. 2,571,151, of which I am a coinventor. It isbelieved, therefore. that-it is unnecessary to discuss the recovery ofthe oxygenated products in detail in this application since referencemay be made to the aforesaid copending applications if necessary.

The following table shows the operating conditions and resulting yieldsand selectivity for various typical runs for ft 1 an iron catalysthaving 0.3, 0.6, and 1.4 percent K20 content, respectively. The fiveruns illustrated were selected as representative of the various runsmade in determining the characteristics of the catalyst.

Table II COMPARISON OF HIGH AND LOW ALKALI CATALYSTS YIELDS ANDSELEOIIVITY Alkali Content, Percent K20 1.4 0.6 0.6 0.3 0.3

Operating Conditions:

Pressure, p. s. i 250 250 250 250 250 Temperature, F 030 570 595 555 565Space V lcity V Hl'./V 470 700 1.150 O. F /IEl'.r./Lb Fo 15 21 t 59. 0Recycle Ratio. Rec/l. 1. 1. 5 1. 9 HnCOin Fresh Fced 1.4 1.4 1.8 H 100in Inlet 2.3 2. 4 2. 4 'CO Conversion, Percent..." 90 90 86 Yields,Basis Fresh Feed, cc./m

Total Hydrocarbons 149 169. 5 165 125 111 Oxygenated Compounds. 47 12 8S Total liquid organic compounds 196 181. 5 177 133 119 Y atcr 102 108108 70 90 Selectivity, Percent:

(JO-)CO 30. O 30. 5 30. 5 32. 3 2T o0- 0Hi 5.8 s. 4 10. 1 P 0 Q888-)(C3. 9.2 7.4

a 9. 5 8. 0 (JO- 01 6.7 5.4 s. 6 i OO C5. 6. 6 8. 9 9. 1 Egg- 85- 3.95.1 4.8

1- 2. 9 4. 5 4. 1 (lo-+08" 1.3 3.5 2.6 22 (JO- 00... 1. 6 3. 6 Z. 7CO-)01o+ 8.4 11.7 7. 8 OO Oxygenatcd Compou 13. 6 0 3.0 2.0 2 0 CO-.Liquid Organic pounds 55. 0 53. 7 50. 6

1 Based on total fresh feed (OO-i-Hz). 1 Inert free.

The results obtained with the various catalysts containing differentpotassium oxide contents indicated that the catalysts containing thesmaller amounts of alkali were most active in the conversion of carbonmonoxide. The relative activity is seen in the foregoing table in thefact that the high alkali catalyst required a higher temperature and alower space velocity to obtain approximately the same amount of COconversion as the lower alkali catalyst.

A comparison of the yields and of the selectivity of the three catalystsis also found in the foregoing table. No allowance has been made forpossible losses in the various recovery systems. xamination of Table 15indicates that the catalyst containing a higher amount of alkaliproduced more than four times as much oxygenated compounds as did thelower alkali catalyst. Generally, the high alkali catalyst had aslightly lower hydrocarbon yield than the lower alkali catalyst. Atcomparative space velocities, the high alkali (1.4 percent K20) catalystproduced slightly mone low boiling hydrocarbons than did the 0.6 percentK20 catalyst, but the low boiling hydrocarbons were formed at theexpense of a decrease in yield of 400 F. end point gasoline.

The oxygenated compounds with the low alkali catalyst were predominantlyalcohols and are produced concurrently with the hydrocarbons and areconsidered very valuable products. With the high alkali catalyst, theacid product was almost equal to the alcohol product. The catalystcontaining the 1.4 percent K20 produced a much larger amount ofoxygenated organic compounds than did the other catalyst. For example,the operation shown Alkali Content, K30 percent by weight with the 1.4K20 catalyst resulted in 47 cc./m. of oxygenated compounds as comparedwith the 0.5 percent K20 catalyst and the 0.3 percent K20 catalyst whichproduced 12 and 8 cc./m. respectively. The high alkali catalyst alsoproduced somewhat larger proportions of total liquid products than didthe lower alkali catalyst, as is noted in the Table 11. The relative COdistribution for the various catalysts shown in Table II underSelectivity clearly indicates the greater selectivity exhibited by the1.4 percent K20 catalyst where approximately 55 percent of the CO wasconverted to liquid hydrocarbons and chemicals, as compared with44.553.7 percent for the other catalysts. As previously mentioned theyields of oxygenated compounds were much greater with the high alkalicatalyst than with the low alkali catalyst.

Table Hi shows a comparison of the distribution of the xygenatedcompounds for the 1.4 percent K20 catalyst and the 0.6 percent K20 foroperating conditions given in Table II. The normal straight chainprimary alcohols are substantially the only type of alcohols producedwith either catalyst. The most striking difference between theoxygenated compounds from the two catalysts was in the acid contentwhich was almost negligible with the 0.6 percent K20 catalyst and was ashigh as about 34 percent of the total oxygenated chemicals with the 1.4percent K20 catalyst. It is also noted that there was a shift toward asubstantially larger production of high alcohols with the 1.4 percentK20 catalyst.

Table III COMPARISON OF HIGH AND LO\V ALKALI CATALYSTS OXYGENATEDCOIVIPOUND DISTRIBUTION negligible. 8.6.

5.7. negligible.

Acetic Acid Propionic Acid Butyric Higher Acids Total Acid Esters E PECAI

negligible negligible The comparative olefin contents of the hydrocarbonfractions obtained with the recovery operations conducted in these runswhen employing the 1.4 percent K20 catalyst and the 0.6 percent K20catalyst are found in Table IV. The hydrocarbons from the high alkalicatalyst included more olefins than those from the low alkali catalyst.The difference is particularly noticeable in the low boilinghydrocarbons, i. e., from C2 to C4 hydrocarbons. The light gasolinerecovered from the charcoal absorber had approximately the same olefiniccontent for each catalyst but the heavy oil and wax for the operationwith the high alkali catalyst showed much less unsaturation than did theheavy oil and wax for the low alkali catalyst. This large difference inthe olefinic condition of the heavy oil and wax was probably caused bythe presence of non hydrocarbons, such as alcohols and acids, andtherefore the actual values based on the hydrocarbon alone wouldprobably show much closer agreement; for example, the heavy oil and waxfrom the high alkali catalyst contained 30 to 35 percent oxygenatedcompounds and on the other hand the same material from the low alkalicatalyst contained about 5 or 6 percent oxygenated compounds.

13 x TableIV COMPARISON OF HIGH AND LOW ALKALI CATALYSTS OLEFIN CONTENTOF HYDROCARBON FRACTIONS Alkali Contcnt,K;O percent by weight 1.4 0.00.6 0.3

Space Velocity, C. FJHrJLb. Fe 1 15 21 51 39 Olefins, Percent:

C 70 19 19 Cl 90 64 58 38 C 90 71 68 Adsorber Gasoline (Cs-Cw) 75 72 7060 Heavy Oil+Wax (010+) 52 70 1 Based on total fresh feed (00+Ha).

4 Since in commercial processes the C3 and the C4 olefins could bepolymerized to form polymer gasoline, the distribution of the liquidhydrocarbons after the formation j of lb. R. V. P. gasoline with theincorporation of the lb. R. V. P. gasoline after polymerization while onthe other hand the low alkali catalyst produced an excess amount oflight hydrocarbons amply sufficient for the production of 10 lb. R. V.P. gasoline.

COMPARISON OF HIGH AND The 400 F. end point gasoline inspection are alsosummarized in Table V. For comparative space velocity with the 1.4, 0.6,and 0.3 percent K20 catalyst the yields of gasoline including polymerswas lowest for the 0.3 catalyst and highest for the 0.6 catalyst. The400 F. end point gasoline yield (Ca+) with the added polymer was about20 cc./m. less from the high alkali catalyst than from the lower alkalicatalyst. The large increase in gasoline yield when the catalyticpolymer is included was caused by both the large yield of olefinichydrocarbons and the large yield of relatively low boiling hydrocarbons,such as Ca and C4 hydrocarbons. This was particularly the case with thegasoline produced from the high alkali catalyst where the catalyticpolymer comprised about 34 percent of the total gasoline.

The gasoline from the lower alkali catalyst was of a higher quality thanthat from the high alkali catalyst. Comparative results are shown inTable V for the raw gasoline including polymers and the gasoline aftertreatment of the naphtha fraction with activated alumina at 850 F. todestroy by dehydration, decarboxylation, etc., any oxygenated compoundspresent.

The data clearly indicates the improvement in gasoline quality by thealumina treating at 850 F. It was noted that the high alkali catalystproduced a gasoline which was not as susceptible to improvement by thealumina treatment as was the gasoline pnoduced with the low alkalicatalyst.

Table V LOW ALKALI CATALYSTS HYDROCARBON YIELDS AND PRODUCT QUALITYAlkali Content, K10 percent by Weight 1.4 0.6 0.6

Space Velocity, O. FJHr. Lb. Fe (Fresh Feed). 15 21 51 GasolineComposition, Vol. Percent:

04 8 1 3.5 1.5 Light Naphtha (100% C5) 21. 4 35. 0 47. 7 Heavy Naph a41. 6 42. 5 26. 9 Catalytic Polymer (2# RVP) 33. 9 19. 0 23. 9 Qualityof Gasoline (+P0ly.):

Reid Vapor Pressure, p. s. i l 9. 2 10.0 10.0

Raw Treated 1 Raw Treated 1 Raw Treated 1 Octane Number- A TM-Clear 73.0 ASTM +3 cc. TEL/Ga 81. 0 Quality of Diesel Oil (400650 F Max. Pour, F+10 Flash Point, PMOC, F 185 SSU Viscosity at; 100 F., Sec. 35.0 DieselIndex 72 1 Insuflicient C4s to make 10# Reid. 1 A120! at 850 F.

Table VI COMPARISON OF HIGH AND LOW ALKALI CATALYSTS DIESEL OIL QUALITYAlkali Content, K,O percent by weight.. 1. 4 0. 6 0. 6 0.6 0. 6

Treated Diesel Oil Inspections Raw 1 Raw Hydro- A110; and HygenatedTreated drogenated Gravity API 42 1 44 9 46.3 44 8 46.0 ns'rMbistillation, 11:

IBP 388 369 410 450 423 10%. 461 451 464 460 44 4 493 472 480 472 468510 496 505 500 492 557 533 546 536 531 611 589 600 596 589 E. P 650 640644 650 627 Bromine N0., gmJlOO gm 42 1 44 1 2. 2 45 4 1 4 AnilinePoint, F l 111 154 178 101 180 Max. Pour, F +20 +5 +20 +10 +15 FlashPoint, PMOO, F 196 160 204 187 SSU Viscosity at 100 F., S 35 4 34. 935.9 35 0 34 9 Diesel Index 47 69 82 1 Partially extracted with ethyleneglycol.

A comparison has been made in Tables 'V and VI of the :quality of 400 F.to 650 F. Diesel oil produced with the 1.5 and the 0.6 percent Kcatalyst. The diesel fraction from the low alkali catalyst was inspectedraw, after hydrogenation of the raw diesel oil, after alumina treatmentat 850 F., and after alumina treatment followed by hydrogenation. Thehydrogenation material was of particularly good quality. The untreateddiesel oil from the high alkali catalyst which had been glycol extractedto remove oxygenated compounds had an inferior diesel index. This wasprobably caused by the lower aniline point, which in turn was caused bythe presence of alcohols and acids not removed by the glycol extraction.

The C3 and C4 hydrocarbons from the low alkali catalyst are in excess ofthat needed to produce 10 lb. R. V. P. gasoline while on the other handthe high alkali catalyst produced insuflicient low boiling hydrocarbonsto produce 10 lb. R. V. P. gasoline after polymerization. The quality ofboth the gasoline and the diesel oil is indicated on Tables V and VI,and was much superior when produced with a low alkali catalyst.

The product water from the high alkali catalyst operation using a 1.4percent K20 catalyst contains a large concentration of organicoxygenated chemicals, such as acids, alcohols, ketones, aldehydes, andesters. Additional water soluble chemicals were dissolved in the heavyoil and could be removed by water washing. The oil also contained waterinsoluble material. The separation, analysis, and identification of theoxygenated compounds in the water was accomplished primarily by precisefractionation, sometimes followed by preparation and examination ofderivatives. To simplify the separation and recovery problem, the acidswere first neutralized with caustic. Below are listed some of thecompounds and azeotropes which were identified from the distillationcurve by their boiling points and by analogy with previousdistillations.

Acetaldehyde Acetone-Methanol Methanol Ethanol-Ethyl acetateEthanolMethyl ethyl ketone Ethanol-Water Propano1-Water Butanol--Water15 pounds produced with the 1.4 percent K20 catalyst are shown in TableVII below.

Table VII Aldehydes: Vol. percent Acetaldehyde 1.6 Propionaldehyde 0.6Butyraldehyde and higher 7.1 Ketones:

Acetone 0.9 Methyl ethyl ketone 0.5 Pentanone and higher 2.0 Esters:

C3 ester 1.0

C4 ester 1.2 C5 ester and higher 6.6 Alcohols:

Methanol 1.2

Ethanol 25.8 Propanol 5.2 Butanol 4.0 Pentanol 1.7 Hexanol and higher7.1 Acids:

Acetic 9.8

Propionic 4.6 Butyric 4.5 Valeric 2.6 Caproic and higher 12.0

The average distribution of total oxygenated compounds was about percentin the product water and gas and about 40 percent in the oil. Ethanolwas the most abundant of the non-acids produced and of the acids thelighter acids were most predominant, i. e., acetic, propionic, andbutyric.

In the operation using the high alkali catalyst con taining 1.4 percentK20 several catalyst samples were withdrawn from the reactor duringoperations to determine changes in analysis of the catalyst as thecatalyst age increased. Oil and wax deposits were removed from thecatalyst by xylene extraction. A sample of the extracted catalyst wasnext burned in a combustion tube in an atmosphere of oxygen and theresulting CO2 measured to determine carbon. Another oil and wax freesample was used for chemical determination of iron. Data obtained fromthese analytical procedures and size analyses are shown in Table VIII.

Table VIII POWDERED IRON CATALYST 1.4% K10 ANALYSES Run Fresh Recharge 12 3 4 5 6 Discharge Catalyst Age, Hours 0 372 545 611 721 761 804 882931 Operating Conditions:

Temperature, F 580 590 586 590 610 633 628 6330 Pressure, 1). s. 1-8-250 250 250 400 250 250 250 250 Inlet 11 200...- 2.5 2.3 2.1 2.5 2.31.9 2.1 2.8 Analysis:

OiH-Wax, Percent 0 14. 1 9. 8 26. 0 27. 3 12.6 10. 1 6. 9 7. 6 Carbon 017. 1 18. 9 15. 8 16. 3 22.0 23. 4 23. 6 24. 0 .4 50. 9 40. 7 43. 3 45.0 55. 2 53. 8 58. 0 60. 0 .0 9.1 21.5 7.7 5.2 2.7 7.8 2.8 1.0

' "6.1? III: III: III IIIIIIII IIIIIIII IIIIIIII ZIIIIIII 57. 9 57. 449. 3 49. 1 57. 2 57. 9 60. 1 60. 7 173 174 203 204 175 167 1 165 Lb.(3/100 Lb Fe 29.5 32.9 32.1 33.1 38. 5 39.1 39.3 39.5

The above compounds and azeotropes collectively accounted for about 16percent of the high alkali catalyst water product of which about 7.5percent or 47 percent of the overhead was ethyl alcohol-Water. Less inquantity was the propanol-water alcohol amounting to about 2 /5 percentor 16 percent ,of the overhead.

An analysis and distribution of the oxygenated com- From the data inTable VIII it is evident that a high alkali catalyst could be operatedat relatively high temperatures (630 F.) without excessive cokeformation. A period of very small change in carbon formation wasattained after about 400 hours and maintained for an additional 350hours. With the low alkali catalyst containing 0.6 percent K20, asimilar steady state was reached after about 450 hours and maintainedfor about 200 hours. This steady state condition with the low alkalicatalyst was about 23 lbs. c./ 100 lbs. of iron while with the highalkali catalyst it was about 33 lbs. c./100 lbs. of iron. An estimate ofthe relative volumes of original and approximately steady state catalystindicated that the latter material would occupy nearly four times theoriginal volume.

In Table IX is tabulated operating conditions and yields for the variouscatalysts having different alkali contents and 150 pounds per squareinch pressure. Table IX is very similar to Table II but contrary toTable II the operating pressure was 150 pounds per square inch insteadof 250 pounds per square inch. From this data presented in Table IX itis evident that the yield of oxygenated compounds with the high alkalicatalyst is much larger than the low alkali catalyst even at lowpressures of about 150 pounds. The discussion of Table II will apply inmost respects to the analysis of the data in Table IX and consequentlyfurther discussion of Table IX is deemed unnecessary. It should benoted, however, that the data in Table IX substantiates the data inTable II and the discussion in connection therewith. The analysis of theoxygenated compounds, the gasoline fractions, and various otherfractions as discussed in connection with the 250 pound pressureoperations was found to be quite similar with the 150 pound operation asshown in Table IX below:

Table IX K20, percent by weight 0.7 0.3 1.4

Operating Conditions:

Hours on condition 34 235 Pressure, p. s. i 150 150 150 Temperature, F560 590 583 Space Velocity- V./Hr./V 415 1, 525 C. F./Hr./Lb./Fe 21. 639. 9 18. 9 Recycle Ratio Re/tl No 1. 8 1. 17

Recycle H1: Fresh Feed 2.0 1. 6 1. 6 HFCO Inlet 2.0 2.15 2.4Contraction, percent 52. 8 52.8 53.0 C0 Conversion, Percent; 93.1 89. 787. 2

Yields, Basis Fresh Feed ce.s per Cubic Meter: 1

1 Cubic centimeters per cubic meter or total fresh feed.

Although the reduced ferruginous catalyst of this example has beenconsidered to have an ultimate composition of metallic iron and K20, theactual composition of the catalyst may contain considerable amounts ofunreduced oxides of iron. For convenience and clarity the K20 content iscalculated on the basis that all the Fe in the catalyst is present asmetallic iron. Also, although the potassium content of the catalyst isreported as K20, the potassium may be present in other forms than K20.

Various minor modifications of the apparatus and specific conditions ofreaction may become apparent to those skilled in the art withoutdeparting from the scope of this invention.

Having described my invention, I claim:

1. A fused hydrogenation catalyst comprising iron containing between 0.1and 1.5 weight percent potassium oxide based on metallic iron.

2. A fused hydrogenation catalyst comprising iron and between 0.1 and1.5 weight percent of a promoter selected from at least one member of agroup consisting of an alkali metal compound and an alkaline earthcompound, the weight percent of the promoter being calculated as anoxide thereof based on iron.

3. A fused hydrogenation catalyst comprising elementary iron and between0.1 and 0.7 weight percent of a promoter selected from at least onemember of a group consisting of an alkali metal compound and an alkalineearth compound, the weight percent of the promoter being calculated asan oxide thereof based on iron.

4. A fused hydrogenation catalyst comprising elementary iron, andbetween 0.8 and 1.5 weight percent of a promoter selected from at leastone member of a group consisting of an alkali metal compound and analkaline earth compound, the weight percent of the promoter beingcalculated as an oxide thereof based on iron.

References Cited in the file of this patent UNITED STATES PATENTS1,148,570 Bosch et al Aug. 3, 1915 1,618,004 Greathouse Feb. 15, 19271,801,382 Wietzel Apr. 21, 1931 2,292,570 Klemm et al. Aug. 11, 19422,391,283 Weber et al Dec. 18, 1945 2,398,462 Roelen et al. Apr. 16,1946 2,438,584 Stewart Mar. 30, 1948 2,474,845 Jenny et al July 5, 19492,488,150 Walden et a1. Nov. 15, 1949 2,537,699 Pierce Ian. 9, 1951

2. A FUSED HYDROGENATION CATALYST COMPRISING IRON AND BETWEEN 0.1 AND1.5 WEIGHT PERCENT OF A PROMOTER SELECTED FROM AT LEAST ONE MEMBER OF AGROUP CONSISTING OF AN ALKALI METAL COMPOUND AND AN ALKALINE EARTHCOMPOUND, THE WEIGHT PERCENT OF THE PROMOTER BEING CALCULATED AS ANOXIDE THEREOF BASED ON IRON.